Null pointer exception no MockResult

@Before
    public void setUp() {
        
        collabletInstance = mock(CollabletInstance.class);
        tagMgrInstance = mock(TagMgrInstance.class);

        result = new MockResult();

        controller = new TagMgrController(result);
    }

    @Test
    public void shouldAddCollabletInstanceToResultForMethodList() {
        when(tagMgrInstance.listAll()).thenReturn(fakeTwoTagsList());
        
        controller.list(collabletInstance, tagMgrInstance);
        assertEquals(collabletInstance, result.included("collabletInstance"));
    }

    private List<Tag> fakeTwoTagsList() {
        Tag tag1 = new Tag();
        tag1.setId(1L);
        tag1.setName("manager");

        Tag tag2 = new Tag();
        tag2.setId(2L);
        tag2.setName("desenvolvedor");

        List<Tag> tagsList = new ArrayList<Tag>();
        tagsList.add(tag1);
        tagsList.add(tag2);
        return tagsList;
    }

@Get
    @Path(value="/groupware-workbench/{collablet}/tagMgr/{tagMgr}")
    public void list(final CollabletInstance collablet, final TagMgrInstance tagMgr) {    
        result.include("collabletInstance", collablet);
        result.include("tagList", tagMgr.listAll());
        result.use(Results.representation()).from(tagMgr.listAll()).serialize();
    }